A User Suspects Someone Has Been Accessing a Home Network

A user suspects someone has been accessing a home network without permission by spoofing the MAC address of an authorized system. While attempting to determine if an authorized user is logged into the home network, the user reviews the wireless router, which shows the following table for systems that are currently on the home network. Which of the following should be the NEXT step to determine if there is an unauthorized user on the network?

A) Apply MAC filtering and see if the router drops any of the systems.
B) Physically check each of the authorized systems to determine if they are logged onto the network.
C) Deny the "unknown" host because the hostname is not known and MAC filtering is not applied to this host.
D) Conduct a ping sweep of each of the authorized systems and see if an echo response is received.